This application is related to Japanese Patent Application No. 2000-367754 filed on Nov. 29, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an adjustment pipe for adjusting a compression amount of a spring biasing a valve member in a fuel injection valve, and a press-fitting structure and a press-fitting method of the adjustment pipe.
2. Description of Related Art
In a fuel injection valve, generally, a valve member (needle valve) for opening and closing a fuel injection port is biased by a spring, and a spring force of the spring is adjusted by an adjustment pipe disposed in a cylindrical housing. For fitting the adjustment pipe within the cylindrical housing, a caulking method or a press-fitting method may be used. In the caulking method, an outer radial dimension of the adjustment pipe is made slightly smaller than an inner radial dimension of the cylindrical housing, and the cylindrical housing is fastened and deformed to fix the adjustment pipe after the adjustment pipe is inserted into the cylindrical housing. On the other hand, in the press-fitting method, the outer radial dimension of the adjustment pipe is made slightly larger than the inner radial dimension of the cylindrical housing, and the adjustment pipe is fixed into the cylindrical housing by press-fitting the adjustment pipe into the cylindrical housing. In this case, when a fixing load (press-fitting load) of the adjustment pipe relative to the cylindrical housing is made larger for tightly fixing the adjustment pipe, the adjustment pipe and the cylindrical housing are strongly rubbed to each other, and an xe2x80x9cadhesionxe2x80x9d due to strongly rubbed metals is readily formed. Therefore, the press-fitting load is excessively increased, components such as the cylindrical housing may be deformed, and dimension accuracy of the components in the fuel injection valve may be decreased.
In view of the foregoing problems, it is an object of the present invention to provide an adjustment pipe for adjusting a compression force of a spring in a fuel injection valve, and a press-fitting structure of the adjustment pipe into a cylindrical housing, which can sufficiently maintain a dimension accuracy of the fuel injection valve.
In is an another object of the present invention to provide an adjustment pipe being press-fitted into a cylindrical housing in a fuel injection valve, which reduces a difference of press-fitting load of the adjustment pipe, readily performs a fine adjustment of a press-fitting amount of the adjustment pipe, and restricts a compression deformation of components of the fuel injection valve.
It is a further another object of the present invention to provide a press-fitting method for press-fitting an adjustment pipe into a cylindrical housing for a fuel injection valve, by which a high-quality and trustworthy fuel injection valve can be readily manufactured.
According to the present invention, in a press-fitting structure of an adjustment pipe for adjusting a compression amount of a spring member for biasing a valve member, a lubricating material is adhered or formed on at least one of an outer peripheral surface of the adjustment pipe and an inner peripheral surface of a cylindrical housing. Therefore, when the adjustment pipe is press-fitted into the cylindrical housing, because the lubricating material is placed between the adjustment pipe and the cylindrical housing, it can prevent a direct pressure-contact between both metal press-contacting surfaces of the adjustment pipe and the cylindrical housing, and it can restrict the adhesion from being generated. In addition, because the lubricating material is placed between the adjustment pipe and the cylindrical housing, the lubricating material does not increase a press-fitting load. Accordingly, a difference of the press-fitting load of the adjustment pipe can be made smaller, a fine adjustment of the press-fitting amount of the adjustment pipe can be made simple, and compression deformation due to an excessive press-fitting load can be restricted. Accordingly, when the press-fitting structure of the adjustment pipe is used for a fuel injection valve, a dimension accuracy of the fuel injection valve can be sufficiently maintained.
Preferably, each of the adjustment pipe and the cylindrical housing is made of stainless steel, and an oxalate film is formed on at least one of the outer peripheral surface of the adjustment pipe and the inner peripheral surface of the cylindrical housing. Alternatively, a phosphate film is formed on at least one of the outer peripheral surface of the adjustment pipe and the inner peripheral surface of the cylindrical housing. In this case, because the oxalate film or the phosphate film is not removed even when the adjustment pipe is press-fitted into the cylindrical housing, the dimension accuracy of the fuel injection valve can be readily maintained.
According to a press-fitting method for press-fitting an adjustment pipe into a cylindrical housing for a fuel injection valve, after a lubricating material is formed or adhered on at least one of an outer surface of the adjustment pipe and an inner surface of the cylindrical housing, the adjustment pipe is temporarily press-fitted into the cylindrical housing, and the press-fitted amount of the adjustment pipe into cylindrical housing is adjusted to a predetermined amount. In addition, a test liquid is supplied into a temporarily assembled fuel injection valve, and a confirmation operation of a fuel injection amount from the fuel injection port is repeated by opening and closing the valve member while the adjustment pipe being gradually press-fitted into the cylindrical housing. Accordingly, a stable fixing load of the adjustment pipe can be obtained, and a high-quality fuel injection valve can be readily manufactured.